PROJECT SUMMARY/ABSTRACT Triple negative breast cancer (TNBC; estrogen receptor-, progesterone receptor- and HER2-negative) is the deadliest sub-type of breast cancer. However, relative to other breast cancer sub-types, TNBCs can be found with many tumor infiltrating T cells. The presence of these T cells suggests a response to tumor-associated antigens. From this response, some of the tumor-specific T cells proliferate and differentiate into effector, central, or tissue-resident memory T cells. The central memory T cells are long-lived and can be found surveying the body for the offending antigens. It was recently shown by Dr. Borges and others that the risk of mortality from TNBC sharply decreases 5 years after diagnosis. However, it is unknown which patients will respond successfully to therapy and which patients will recur. Thus, there is an urgent need to determine how these T cells can be harnessed for future therapies. It is proposed here to identify shared T cell receptors of TNBC survivors of five or more years and patients undergoing therapy. The overall goal of the proposed research is to improve treatments for TNBC patients using a method recently developed by the Slansky and DeKosky labs. They performed studies using high throughput sequencing, and found a panel of TCRs common to HLA-A2+ breast cancer patients, but not healthy controls. The T cell receptors shared in tumors were also identified in the peripheral blood of these patients. The overall objective of this application is to use the repertoire of alpha-beta memory CD8 T cells to identify a shared T cell response among responder patients and to determine the influence of standard therapy on T cells. The central hypothesis addressed here is that common subsets of TCRs can be identified that are unique to the blood of women who have survived TNBC more than 5 years, but not blood of women who have recurred. The specific aims to address this hypothesis are: (1) to identify T cell receptors of shared memory T cells from the blood of TNBC survivors, and (2) determine longitudinal changes in the memory T cell repertoire that correlate with a pathologic complete response after treatment. Using the T cell repertoire to understand the generation of long-term memory responses to TNBC may ultimately revolutionize treatment for TNBC, as it will provide the first steps toward identification of T cell receptors that may be used to determine antigens critical to maintaining disease-free survival and other therapies that can offer ongoing protection against recurrence for years into survivorship.